1. Field of the Invention
The present invention relates t inductively heatable reactors suitable for implementing fluid phase reaction processes.
2. Description of Related Art
Various reactor designs are known. It is known, for example, to carry out reaction processes by passing fluid phase reactants through a furnace-heated reactor tube. However, such a reactor provides adiabatic reaction conditions therein and a relatively long reaction time. Consequently, the reactions tend to suffer from the disadvantage of a lack of selectivity towards product formation, and by-products are often formed by competing reactions.
In GB Patents 1182421 and 1325675 fluid heaters having as their essential feature a porous, fluid-permeable, electrical resistance heater element, which can be in the form of a hollow cylindrical body, are described. The heater elements described therein are heated by direct current and arranged so that the fluid to be heated passes through the element from an entry side thereof to an exit side, the hot exit fluid being cooled after it emerges from the element. One drawback of the direct current heating used in the heaters of GB Patents 1182421 and 1325675 (said also to be usable as reactors) is that there may be heat losses due to thermal conduction by way of the leads carrying the current. Additionally, the finely porous nature of the reactor elements would be liable to cause them to foul with reaction products and carbon deposits after relatively short periods of use.
The use of fluid-permeable heater elements that are heated indirectly by electrical induction has been reported in U.S. Pat. Nos. 4,091,021 and 3,826,895, and in GB Patent 1593473. The thermal heater elements described in the two U.S. Patents consist of a felted plug or packing of randomly oriented, electrically conducting fibres (metallised at their points of contact to improve electrical conductivity) which fill most the length of a tube (in the case of U.S. Pat. No. 3,826,895, a plurality of such elements being connected in series); the element of GB 1593473 is of a different design and comprises a packing of touching small metal spheres in a tube. The design and large thickness of the inductively heatable reactor elements described in the aforementioned patents would be unlikely to allow fluid residence times of the order of milliseconds or the substantially uniform thermal treatment of each and every part of the fluid flowing through them. Furthermore, the metallic connections would be subject to chemical attack in an acidic atmosphere at an elevated temperature.
In U.S. Pat. No. 3,428,695 there is described a fluid phase reaction process which is carried out by continuously passing a stream of reactants through an elongated tube. The use of an inductively heated graphite tube reactor (32.5 cms (13") long, internal diameter 0.31 cms (1/8"), outer diameter 1.25 cms (1/2")) centred within a high silica glass tube is specifically described in this U.S. patent, the inductive heating being effected by means of a copper coil supplied with power from a high frequency generator operating at 450 kilocycles. The tubular reactor described in this patent is said to allow short reactor times to be employed. However, such a reactor design is thought to incur a fairly broad reaction time distribution, even if short reaction times are employed, which can lead to a decreased selectivity for the desired reaction product(s) and the formation of unwanted by-products. Furthermore, single bore tubular reactor elements tend to exhibit poor heat transfer characteristics since the surface area of the walls enclosing the reaction zone is small compared to the volume of the reaction zone. Consequently, the uniform thermal treatment of all the fluid reactants passing through the reactor element may be unattainable. Furthermore, the tubular reactor element of U.S. Pat. No. 3,428,695 is not particularly amenable to scale-up, since the problems associated with having a single large hole passing through the reactor element will be accentuated as the dimensions of the reactor element are increased.